1. Field of the Invention
This invention relates to a rotary switch and, more particularly, to a multiposition switch having detent means for positive indexing.
2. Description of the Prior Art
Rotary switches are used to make and break an electrical connection in electric circuits. Achievement of an electrical connection is generally dependent upon the mechanical interaction of the component parts of the switch. In switches utilizing rotary movement, mechanical contact and thereby electrical connection between two electrical terminals is often obtained by rolling members such as conductive balls and rollers or other curved members conducive to the rotation of the switch. Rolling contacts of the rotary type switch are used mainly because they respond to rotational movement with reduced, if not minimum, friction resulting in less wear of the component parts.
A desirable feature of rotary switches is to maintain with certainty that the switch be fixed in a set position once that position has been selected. In order to prevent inadvertent drifting of the switch out of the selected position, certain prior art arrangements employ detent mechanisms or pawling mechanisms. In general, the function of either mechanism is to develop a restraining force between interacting mechanical members, one of which is movable with respect to the other, such that the movable member is selectively locked in a fixed position. The stopping action is selective since the mechanism is arranged to allow the movable member to advance out of one position and into the next when an additional force is applied to overcome the original restraining force. The prior art devices utilizing the detent or pawling mechanisms couple these locking mechanisms to the contact means to thereby index the stopping action such that a fixed position coincides with a make or break electrical connection made.
A disadvantage of certain prior art switches is that they use complex ball or roller contacts and detent mechanisms requiring interaction of many movable mechanical members increasing the potential of failure and the reduction of reliability. Since it is required to maintain the balls or rollers in contact with the electrical terminals in the switch, the prior art devices usually provide a spring force to assure this contact. Various devices utilize a helical or leaf spring for each of the ball or roller contacts employed, whereas other devices include one spring urging a common disc or plate against the ball or roller contacts. The detent mechanisms in these devices generally comprise interacting members such as specially shaped cams, discs with single or multiple tooth-like projections, or ratchet mechanisms.
The interdependence of the spring contact means and the detent mechanism and, consequently, the need to use more parts has resulted in switches too large in size for many applications, and in particular, for printed circuit board applications. The advantage of utilizing printed circuit boards in modern technology is well-known in increased reliability, life, and compactness. Where space is a consideration in the design of an electric circuit, large switches would be inconsistent with the concept of condensation and would require compromises which would be neither necessary nor desired if a compact rotatable detent switch were available.